1. Field of the Invention
The present invention relates to a semiconductor integrated circuit incorporating bypass capacitors connecting power supply wiring to grounding wiring and a semiconductor integrated circuit having a layout designed by the cell base system.
2. Description of the Prior Art
FIG. 33 is a conceptual view showing the layout pattern of a conventional IC including digital portion and an analog portion, FIG. 34 is a sectional view showing an IC package mounted with a conventional IC chip, and FIG. 35 is a perspective view showing a conventional IC package. In respect of FIG. 33, numeral 1 designates an IC chip formed on a silicon substrate, numeral 2 designates a digital portion formed on the IC chip 1 and numeral 3 designates an analog portion formed on the IC chip 1. Numeral 4 designates power supply wiring for the digital portion, numeral 5 designates grounding wiring for the digital portion, numeral 6 designates power supply wiring for the analog portion and numeral 7 designates grounding wiring for the analog portion.
In respect of FIG. 34, numeral 8 designates a package, numeral 9 designates a lead of the IC chip and numeral 10 designates a wire for connecting the lead 9 and the IC chip 1.
An explanation will be given of the operation as follows.
Generally, a semiconductor integrated circuit (hereinafter, referred to as IC) is functionally classified as a digital IC or an analog IC. The digital IC is an IC carrying a logical circuit operating with values of "1" and "0", (logical circuit), a memory, a microcomputer or the like. Meanwhile, the analog IC is an IC dealing with not "1" and "0", but with continuously changing signals such as the intensity of sound or temperature which is often used in a circuit for amplifying current. In using the digital IC and the analog IC in combination, noise generated from the digital IC influences the operation of the analog IC. Normally such a problem is dealt with by attenuating the noise from the digital IC by attaching a capacitor between a power supply terminal and a grounding terminal of the digital IC. The capacitor is referred to as a bypass capacitor.
In recent years, use of an IC with a digital portion and an analog portion (hereinafter, referred to as a digital/analog mixed IC) where a digital IC and an analog IC are integrated, has been increasing, to reduce a number of parts mounted on a substrate with further downsizing of portable communication devices (portable telephone or the like). In a digital/analog mixed IC, even if the power supplies and the grounds of respective circuits of the digital portion and the analog portion are separately installed and a bypass capacitor is attached to the IC, an attenuating of noise similar to that where the digital IC and the analog IC are used in combination, may be difficult to achieve. An explanation will be given of the reason as follows.
Firstly, to separately install the power supply wirings and the grounding wirings of the digital portion 2 and the analog portion 3 as shown by FIG. 33, the power supply wirings 4 for the digital portion and the grounding wirings 5 for the digital portion are installed at the side of the digital portion 2 and the power supply wiring 6 for the analog portion and the grounding wiring 7 for the analog portion are installed at the side of the analog portion 3. Thereafter, bypass capacitors are installed between the leads 9 connected to the power supply wirings and the grounding wirings as illustrated by FIG. 34.
However, the grounding of the digital portion 2 and the analog portion 3 are common since they are formed on the IC chip 1 that is formed on the same silicon substrate whereby the effect of attenuating noise is reduced. Further, the effect of attenuating noise is reduced by resistances of the leads 9, resistances of the wires 10 and contact resistances of these in the IC.
Accordingly, a desired characteristic is difficult to achieve in a digital/analog mixed IC since noise generated at the digital portion 2 influences the analog portion 3.